1. Field of the Invention
The present invention relates to devices for reducing or removing fogging of viewing members such as visors, windscreens and the like.
2. Related Art
It is known to heat viewing members such as motorbike helmet visors or car windscreens (windshields) in order to prevent or remove fogging (or misting) caused by the condensation of water on the cold surface of the viewing member. Typically, heat is provided to the viewing member either from a flow of heated air or by direct heating, e.g. via a resistive heater element carrying an electric current.
Fogging of such viewing members may occur due to condensation of water vapour in breath. This may dangerously restrict the vision of the user/wearer.
CH 636251 discloses a heatable visor. Resistive heating wires are located between two panes of the visor.
GB-A-2401772 discloses a heated visor for a motorbike helmet with an electric heating element embedded in the visor.
DE-A-3229021 discloses a visor heater with an electrically conductive film. The heater is fixed to the visor via slots.
IT 1171812 and U.S. Pat. No. 4,584,721 each disclose a removable heat generating plate having a transparent heat generating film. Part of the film is removed to ensure that the electrode bus leads in properly to the film.
U.S. Pat. No. 6,701,537 discloses a heater element that is removable from the visor it is intended to heat.
U.S. Pat. No. 4,150,443 discloses a fan-driven circulation of air to prevent fogging of sports goggles.
U.S. Pat. No. 4,682,007 discloses a face shield for a protective helmet having an electrically conductive heating circuit printed by screen printing on the inner surface of the face shield.
U.S. Pat. No. 4,868,929 discloses ski goggles with a fine grid of heat generating wire disposed between two layers of the lens of the goggles.
U.S. Pat. No. 5,500,953 discloses a face shield for a helmet. The face shield has an inner face lens and an outer weather lens. An electroconductive film is formed across the entire surface of the inner face lens, to be heated by an electric current.
U.S. Pat. No. 5,471,036 discloses a visor with a transparent coating of conductive film (indium tin oxide) applied. The edges of the film are etched away to prevent electrical contact with the frame of the visor.
The transparent heating films of the prior art have the disadvantage that they must be very thin to be transparent enough to allow a user to see through them. However, in order to provide a useful heating effect, they must carry significant electrical current. This may require a high voltage, which is not desirable.
Furthermore, the heating elements of the prior art are liable to be damaged (e.g. by overheating or scratching) to the extent that the heating functionality of the element may be impaired. This necessitates costly replacement of the visor or other viewing member.
It is also known to provide motorcycle helmet accessories in the form of thin transparent sheets of plastics material having a surface coating of a type that discourages the formation of water droplets on the surface that together cause fogging. Such accessories do not, therefore, prevent the condensation of water on the surface but instead modify the nature of the condensed water to reduce fogging. For such accessories that allow the formation of larger water droplets, these can act like small lenses to distort the image viewed through a motorcycle helmet visor, especially in dark viewing conditions. A further problem with such accessories is that, by definition, the active surface must be exposed. Consequently, there is a serious risk that the active surface with be scratched or abraded during use, reducing its effectiveness in reducing fogging.